Yogapedia explains Sthala Basti

There are two types of basti, the other being jalabasti, in which water is sucked into the anus with or without the use of a tube. Jala basti should be mastered before moving on to sthala basti.

Sthala basti can be performed in different postures, including utkatasana and ardha paschimottanasana,
but a supine position is recommended for beginners.

Sthala basti improves digestion by relieving gas from the
colon. Because poor digestion leads to other problems, sthala basti
can help prevent headaches, improve concentration and promote an
overall feeling of well-being.